1. Field of the Invention
The present invention relates to motor vehicle seats which comprise a seat base that can be adjusted to the user's morphology. Such seats enable to adapt the length provided by the seat base to the user's leg length, to provide a better comfort by supporting the thighs all the way to the knee bend.
2. Discussion of Prior Art
For this purpose, known seats comprise a seat base in which only the central portion of the seat cushion has an adjustable length, the stuffed lateral sides of the seat base remaining fixed. To be able to adjust this cushion length, it is known to move only the front portion of the cushion, or seat nose, backwards or forwards.
Known systems comprise a seat nose support plate assembled to slide backwards or forwards on a seating frame front crosspiece. The plate is assembled on a carriage sliding in a guide rail placed on the crosspiece.
DE19826823 discloses an adjustment system in which the opposite edges of the carriage are guided in lateral grooves of the guide rail. Said grooves are thus very distant from each other, especially as compared with their length. The system described in this document aims at avoiding for the sliding carriage supporting the seat nose to block by buttressing between the guide rail edges, due to the small length of the guide rail as compared with its width. This system uses a set of four toothed wheels meshing with one another, rotatably assembled on the carriage and aligned transversely to the sliding direction. The two end toothed wheels, which have the same dimension, also mesh with racks respectively provided on each edge of the guide rail. Thus, the displacements of the carriage are necessarily identical on both sides and the carriage thus cannot get stuck by buttressing in the guide rail. The locking in position is ensured by a pivoting lock located towards the back and engaging with one of the intermediary toothed wheels.
A disadvantage of such a system especially is the relatively large number of wheels, required to avoid the above-mentioned buttressing. Further, the unlocking requires operating the pivoting lock located towards the back with complementary control means enabling to control the pivoting of the lock from an offset driving member accessible to the user, which complicates the system manufacturing.
DE-A-102004030363 describes a system for setting the seat base length which comprises a carriage (1) slidably driven by a motor (27) which drives a pinion meshing with a rack (21) fixed on the seat frame. The carriage is guided on guide rails located laterally on either side of the seat.
The present invention especially aims at solving the above-discussed problems. It more specifically aims at providing a system which is easier to form and to use, while suppressing buttressing risks. It also aims at enabling to keep the largest possible seat nose cushioning thickness, by limiting to a minimum the thickness of the adjustment system. It further aims at enabling to use the largest possible number of common parts for a manually-operated adjustment system or a motor-driven adjustment system.